08-08-2012, 09:57 AM
MODEMS
[attachment=30474]
RANGE
Short Haul :
Work in short ranges - up to 15 km (called ‘local loops’)
Are distance-sensitive - signal attenuation occurs
Transmission rate lower to ensure consistent , error-free transmission.
Voice Grade :
Used for unlimited destination, using high data rate
Are expensive and maintenance and tuning are sophisticated
Wide Band:
Used in large volume telephone-line multiplexing, dedicated links.
Exceed high data rates
OPERATION MODE
Simplex :
Communication is Unidirectional. One station can transmit and other can receive.
Examples of simplex are keyboard , monitor, printer etc.
Half Duplex :
Each station can both transmit and receive, but not at same time
At a time, if one device is sending, other can receive and vice versa
Example of half duplex are walkie-talkie
Full Duplex :
Also called DUPLEX
Can transmit and receive simultaneously at full speed
Full duplex modems will not work on half-duplex channels
SYNCHRONIZATION
Asynchronous :
Can only handle data bytes with ‘start’ and ‘stop’ bits
No separate timing signal or clock b/w modem and DTE
Can be connected in different options to the communication media
Using 2-Wire or 4-Wire interface.
Using switched lines or leased lines.
Using interface to call unit/automatic answer, when dialing-up
TYPES OF MODEMS
INTERNAL MODEM
EXTERNAL MODEM
CABLE MODEM
FAX MODEM
WIRELESS MODEM
POKET MODEM
ISDN MODEM
DSL MODEM
56K MODEM
SPEED OF MODEM
Modem speed is rated in bps (bits per second). So a 56k modem transmits at 56,000 bits per second in theory. While 8 bits make a byte, and 1024 bits equal one kilobits, a 56k modem will transmit a maximum of approximately 7 kilobytes of information every second. A modem will never connect higher than what it is rated for.
[attachment=30474]
RANGE
Short Haul :
Work in short ranges - up to 15 km (called ‘local loops’)
Are distance-sensitive - signal attenuation occurs
Transmission rate lower to ensure consistent , error-free transmission.
Voice Grade :
Used for unlimited destination, using high data rate
Are expensive and maintenance and tuning are sophisticated
Wide Band:
Used in large volume telephone-line multiplexing, dedicated links.
Exceed high data rates
OPERATION MODE
Simplex :
Communication is Unidirectional. One station can transmit and other can receive.
Examples of simplex are keyboard , monitor, printer etc.
Half Duplex :
Each station can both transmit and receive, but not at same time
At a time, if one device is sending, other can receive and vice versa
Example of half duplex are walkie-talkie
Full Duplex :
Also called DUPLEX
Can transmit and receive simultaneously at full speed
Full duplex modems will not work on half-duplex channels
SYNCHRONIZATION
Asynchronous :
Can only handle data bytes with ‘start’ and ‘stop’ bits
No separate timing signal or clock b/w modem and DTE
Can be connected in different options to the communication media
Using 2-Wire or 4-Wire interface.
Using switched lines or leased lines.
Using interface to call unit/automatic answer, when dialing-up
TYPES OF MODEMS
INTERNAL MODEM
EXTERNAL MODEM
CABLE MODEM
FAX MODEM
WIRELESS MODEM
POKET MODEM
ISDN MODEM
DSL MODEM
56K MODEM
SPEED OF MODEM
Modem speed is rated in bps (bits per second). So a 56k modem transmits at 56,000 bits per second in theory. While 8 bits make a byte, and 1024 bits equal one kilobits, a 56k modem will transmit a maximum of approximately 7 kilobytes of information every second. A modem will never connect higher than what it is rated for.